Transformation process of Al-Cu-Li alloy sheets

Abstract

The invention concerns a process to manufacture a flat-rolled product, notably for the aeronautic industry containing aluminum alloy comprising 2.1% to 3.9% Cu by weight, 0.7% to 2.0% Li by weight, 0.1% to 1,0% Mg by weight, 0% to 0.6% Ag by weight, 0% to 1% Zn by weight, at least 0.20% Fe+Si by weight, at least one element chosen from Zr, Mn, Cr, Sc, Hf and Ti, the quantity of said element, if chosen, being 0.05% to 0.18% by weight for Zn, 0.1% to 0.6% by weight for Mn, 0.05% to 0.3% by weight for Cr, 0.02% to 0.2% by weight for Sc, 0.05% to 0.5% by weight for Hf and 0.01% to 0.15% by weight for Ti, the other elements at most 0.05% by weight each and 0.15% by weight in total, the rest being aluminum, in which, notably a flattening and/or stretching is performed with a cumulated deformation of at least 0.5% and less than 3%, and a short heat-treatment is performed in which the sheet reaches a temperature between 130° C. and 170° C. for a period of 0.1 to 13 hours. The invention notably makes it possible to simplify the forming process of fuselage skins and to improve the balance between static mechanical strength properties and damage tolerance properties.

Description

CROSS REFERENCE TO RELATED APPLICATIONS[0001]This application claims the priority to French Application No. 1103155, filed Oct. 14, 2011, and U.S. Provisional Application No. 61 / 547,289, filed Oct. 14, 2011, the contents of both of which are incorporated herein by reference in their entireties.BACKGROUND OF THE INVENTION[0002]1. Field of the Invention[0003]The invention relates to aluminum-copper-lithium alloy products, and more particularly to such products, their manufacturing processes and use, designed in particular for aeronautical and aerospace engineering.[0004]2. Description of Related Art[0005]Flat-rolled products made of aluminum alloy are developed to produce parts of high strength designed for the aircraft and aerospace industry in particular.[0006]Aluminum alloys containing lithium are of great interest in this respect because lithium can reduce the density of aluminum by 3% and increase the modulus of elasticity by 6% for each percent of lithium weight added. For these...

AI Technical Summary

Benefits of technology

[0067]Aging is performed in which said sheet reaches a temperature ranging between 130° C. and 170° C. and preferably between 150° C. and 160° C. for 5 to 100 hours and preferably from 10 to 70 hours. Aging may be performed in one or more stages.

[0068]Advantageously, cold working is carried out by one or several forming processes such as drawing, stretch-forming, stamping, spinning or bending. In an advantageous embodiment of the invention, forming takes place in three dimensions to obtain a part of complex shape, preferably by stretch-forming.

[0069]The product thus obtained through short heat-treatment can be formed as an O-temper product or a W temper product. However, compared to an O-temper product, it has the advantage of no longer requiring solution heat-treatment or quenching to attain the final mechanical properties, as simple aging is sufficient. Compared to a W-temper product, it has the advantage of being stable, and does not require a cold room and does not pose problems associated with deformation from this temper. The product also has the advantage of generally not generating unacceptable Lüders lines during forming. The short heat-treatment can thus be performed on the sheet manufacturer's premises and forming can take place on premises of the aeronautic structure manufacturer, directly on the product delivered.

[0070]Surprisingly, the balance between the static mechanical properties and the damage tolerance properties obtained following aging is advantageous compared to that obtained by a similar treatment not comprising a short heat-treatment. The inventors noted in particular that the mechanical strength, particularly the tensile yield strength Rp0.2 (L) is high and increases with the

Problems solved by technology

Generally speaking, after solution heat-treatment and quenching, the sheets are in a state characterized by good formability, although this state is unstable (“W” temper), and forming must take place in an as-quenched condition, i.e. inside a brief delay after the quench, from roughly ten minutes to a few hours.

If this is not possible for production management reasons, the sheet must be stored in a cold room at a sufficiently low temperature and for a sufficiently short duration to avoid natural maturation.

In certain cases, it is noted that for excessively short durations after solution heat-treatment, Lüders lines appear after forming, which requires an additional requirement with a minimum waiting period.

For voluminous and highly formed parts, this solution heat-treatment requires large-scale furnaces, which makes the operation cumbersome, including in relation to the same operation perfo

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